My Nikons - D70, D80, D300, D800 all have a maximum long exposure of 30 seconds (as far as I can gather) and to do a longer exposure I have to use Bulb mode, which means physically pressing the shutter button, which can introduce shake.

Have I missed a setting? or is 30 seconds the limit of automatic long exposure?

2 Answers
2

It is simply a convention because 30s was deemed a reasonable limit. Nikon, Pentax and Sony all use 30s but Olympus uses 60s. Panasonic uses 60s on most camera but up to 250s.

As you can tell by the presence of Bulb mode, most cameras can do more. Olympus limits theirs to 30 minutes to avoid the sensor over-heating or building up too much noise. Other brands can expose for hours.

Note that the available range of shutter-speeds depends on the mode. In Manual mode, you can choose any. However, in modes which rely on metering (S, T, A, P, TAv, etc), you often have a shorter limit (1s to 4s is common). An even more bizarre variation are those DSLRs which have a different limit in Live-View than otherwise.

For automatic metering, the issue is sensitivity of the metering system. At some point, there is not enough light to meter and so the camera cannot know if it needs a 30s, 45s or 1200s exposure.

There may be a practical reason too - but this is speculation - and that is in case the exposure goes to 30s (or more, depending on your camera), you do not have to wait so long for the next shot since most cameras do not let you interrupt an exposure.

Thanks - I really find it odd that there isn't a simple manual entry mode eg next to bulb where you can just set say 48 seconds and leave it to it. Might be a nice little thing for someone do do in a custom firmware (wink wink nudge :-) - D800 please!)
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Darkcat StudiosDec 29 '12 at 18:27

I imagine that this has a lot to do with the arbitrary/artificial limit. They can sell you more things (and those things, especially the name brand intervalometers, can be quite expensive).
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tenmilesDec 29 '12 at 18:21